Automatic liquid fuel burner control



' Filed Dec. 2. 1965 1966 J. MARTIN 3,269,448

AUTOMATIC LIQUID FUEL BURNER CONTROL 2 Sheets-Sheet 1 OIL OIL RETURN SUPPLY HG. g

FIG. 2

INVENTOR JOHN MARTIN 4 j Z 4" CONTROL VENT BY ,//w Mil/MW AIR ATTORNEYS,

Aug. 30, 1966 J. MARTIN AUTOMATIC LIQUID FUEL BURNER CONTROL 2 Sheets-$heet 2 Filed Dec. 2, 1965 INVENTOR JOHN MARTIN ATTORNEY$ United States Patent l 3,269,448 AUTQMATIC LIQUID FUEL BURNER QGNTROL John Martin, Monterrey, Nuevo Leon, Mexico, assigncr to Fabricacion de Maqninas, Monterrey, Nuevo Leon, Mexico, a corporation of Mexico Filed Dec. 2, 1965, Ser. No. 511,167 2 Claims. (Cl. 15828) This invention relates to liquid and gaseous fuel burners and more particularly to a fuel-air control arrangement for a burner of the so-called return fuel flow type.

While it is known to make the fuel supply delivery valve a slave of the combustion .air supply, it has always been a problem to establish a control means which will yield uniform results over a substantial range of B.t.u. outputs for a given burner. Particularly in the case of burners which are adapted to burn oil as a fuel, this problem is even more acute.

Accordingly, it is the principal object of the present invention to provide a control arrangement for a liquid fuel burner which is fully automatic in ope-ration and which yields uniform combustion results over a wide range of B.t.u. outputs of the burner in question.

Other objects of the present invention will become apparent to those skilled in the art from a consideration of the follow-ing detailed description when read in conjunction with the attached sheets of drawings in which:

FIGURE 1 is a sectional view of a liquid fuel burner of the type to which the present invention is addressed;

FIGURE 2 is a sectional view of a diaphragm operated valve which is useful in the control circuit of the present invention; and

FIGURE 3 is a schematic diagram of the air, fuel an electrical circuits for automatic operation of a burner in accordance with the present invention.

In general, the objects of the present invention are achieved by tapping off from the main combustion air supply line to provide an air control line which is connected to a modulating valve which modulates the flow of fuel into the burner. Particularly as it applies to the burning of liquid fuel, the present invention finds pri mary utility in controlling the flow of liquid fuel to the burner at all burning rates and particularly for low burning rates corresponding to low B.t.u. outputs of the burner. This is achieved by providing, between the oil supply line and the return oil flow line, a fixed orifice which insures a proper flow through the fuel modulating valve down to very small B.t.u. outputs of the burner.

Referring now to FIGURE 1 of the attached drawings, this illustrates the type of liquid fuel burner with which the apparatus of the present invention finds primary utility. As mentioned hereinbefore, this burner is of the socalled return fuel flow type. 'As shown in this figure, the burner comprises an elongated structure which includes a refnactory lined combustion chamber having a re duced opening 12 at the outer end thereof. Liquid fuel, for example oil, is fed to the nozzle l4 through the oil supply line indicated and the fuel is at least partially atomized by the nozzle 14 and mixed with combustion air which enters through the passageway 16. The atomized mixture is ignited by any conventional means shown as a spark plug 18 and combustion commences within the tube 20 and proceeds from left to right into the large portion of the refractory lined combustion chamber 10. Due to the reduced opening 12 at the opposite end of the combustion chamber, a certain back pressure is built up which is transmitted from right to left in this figure through the openings 22 in a pair of spiders 23 which support the small combustion tube 20. A portion of the burning mixture of fuel and air is thereby reinjected into the small tube 20 where it aids further in atomization and gassifi- 3,269,448 Patented August 30, 1956 cation of the liquid fuel droplets issuing from the nozzle 14. The net result is that at least of the combustion takes place within the burner itself and the only thing that issues from the exit end of the combustion chamber 10 is a very hot gas. The supply of liquid fuel to burners of this type is always in excess of the ability of the nozzle 14 to issue such fuel in atomized form into the combustion area and for this reason a part of the fuel which goes in the oil supply is returned through the oil return line and hence the name return fuel fiow burner. It is because of this injection and return of fuel that a very fine degree of control may be exerted over the B.t.u. output of the burner.

Turning now to FIGURE 3 of the attached dnawings for a description of the control apparatus of the present invention as applied to a burner of the type shown in FIGURE 1, the burner is indicated at B. The source of both combustion and control air is indicated by the motor driven pump 30 which is connected to the combustion air inlet of the burner through a line 32. Interposed in the line 32 between the pump and the burner is a modulating valve 34, the setting of which is under the direct control of an instrument 36 which sends out pneumatic signal through the line 38 to the valve 34 depending upon the temperature of the temperature sensing means 49 which is immersed in the material to be heated by the burner B. The flow of primary combustion air, therefore, is under the direct and automatic control of the instrument 36 so that the how of such air is modulated in accordance with the work to be done by the burner on the substance in which the sensing means 40 is immersed.

The oil is supplied to the burner from a motor driven pump combination 48 and the high side of the pump is connected to the burner B through a line 50. The oil return line from the burner B is identified by the reference numeral 52 and this line leads to a modulating valve 54 which is under the control of air pressure tapped off from the combustion air line 32 through the control air line 56. The output of fuel oil from the modulating valve 54 is to a return line 58 to a sump which is conveniently connected to the sump from which the pump 48 initially supplies the fuel oil under pressure to the burner B.

By placing the modulating valve 54 in the return oil flow line, a very fine degree of control of the burner output becomes possible. Such control will be described in more detail in connection with the preferred embodiment of modulating valve 54 which is shown in section in FIGURE 2. As shown in this figure, it will be seen that the valve 54 comprises a split housing defining upper and lower interior chambers 60 and 62, respectively. The two chambers are separated from each other in airtight manner by means of a diaphragm 64. The valve proper includes a valve seat 66 and a sperical ball valve member 68, both the seat and the valve member being disposed centrally in the lower portion 62 which is below the diaphragm 6 4. The ball is normally biased toward its closed or seated position by means of a spring 76 and the degree of bias is adjustable by means of the tubular housing member 72 housing the spring and which threadedly engages the upper portion of the valve 54. The upper side of the diaphragm 64 is subjected to the pressure of the control air line '56 of FIGURE 3 which is connected to the passageway 74. The under side of the diaphragm is vented to atmosphere through passageway 76. The return fuel line 52 of FIGURE 3 is connected to the passageway 78 which leads directly to the under side of the valve member 68. Thus it will be seen that the oil pressure in the oil return line always acts in a direction to unseat the valve member .68 from its seat 66 and this action is constantly opposed by the pressure on the upper side of the diaphragm due to its connection to the control air line 56 and at lower fuel burning rates by the minor ef- 0 feet of the biasing spring 70. The vent line 79 FIG- URE 3) is connected to the passage 76 of the valve shown in FIGURE 2, and maintains atmospheric pressure in chamber 62 to prevent syphoning of the fuel from the system.

As thus far described, it will be apparent to those skilled in this art that the action of valve 5-4 is such as to control the degree of back pressure in the return line 52 in direct dependence upon the pressure in the control air line 56. In other words, as the demand for heat goes up as sensed by the sensing means 40, and the modulating valve 34 of FIGURE 3 is opened to increase the supply of combustion air to the burner, an increased biasing force is applied to the valve member 68 which has the effect of increasing the back pressure and consequently the fuel flow through the nozzle 14 of the burner FIG- URE 1. The converse is true as the demand for heat drops off.

The diificulty which has been experienced in systems of this kind to date is that at the lower demand for heat from the burner, the action of valve 54 becomes unstable and the ball may in fact tend to flutter on its seat 66. Since it is also desirable to maintain a linear relationship between the demand for heat and the flow of oil to the burner, a fluttering of the valve member 68 is inconsistent with the desired linear relationship. In order to overcome this difliculty, it has been found that the insertion of a fixed orfice between the return oil line 52 and the oil supply line 50 is effective to insure a predetermined pressure on the under side of the ball '68 for even very low rates of fuel flow to the burner B. In practice an orifice 0.010 inch in diameter yields excellent results. In referring again to FIGURE 3, such orifice is indicated in that figure by the reference numeral 80.

Still referring to FIGURE 3, there is an air trim valve 82 positioned in the line 56 and this is merely a pressure reducing valve which is set initially and requires no further adjustment. The same holds true for the valve 86 positioned in the main air line 32 between the modulating valve 34 and the burner B.

The control system above described functions to control the return fuel oil back pressure in inverse relation to the combustion air pressure. The spring 70 furnishes the necessary biasing force for the return fuel oil back pressure in the absence of or at a very low combustion air pressures corresponding to very low B.t.u. output of the burner. Under these same conditions, the orifice 80 is effective to maintain a positive back pressure and therefore a small and steady fuel flow through the fuel oil control valve.

From the foregoing it will be apparent to those skilled in this art that there is herein shown and disclosed a new and useful liquid fuel burner control apparatus which will have utility wherever accurate linear control of fuel air ratios to return fuell flow burners is required. While a preferred embodiment of the present invention is herein shown and described, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

I claim:

1. In a liquid fuel burning system of the type which includes a return fuel flow burner, an automatic air fuel \feed control apparatus comprising in combination:

a source of liquid fuel under pressure and a main line connecting said source to the burner;

a source of primary combustion air under pressure also connected to the burner;

means for controlling the amount of air fed to said burner in accordance with the temperature of a substance to be heated thereby;

modulating fuel valve means mechanically biased toward closed position;

means connecting said source of air to urge said valve toward closed position;

means connecting the return liquid fuel line from said burner to said valve in a direction to urge said valve to open position;

means connected to the opposite side of said valve for returning liquid fuel passing therethrough to said source of liquid fuel under pressure;

and means defining an orifice sized to create a predetermined pressure drop connected between said main liquid fuel line and said return line on the burner side of said valve; whereby the back pressure in the fuel return line is controlled inversely as the combustion air pressure and a positive fuel fiow is maintained for all rates of combustion of the burner.

2. In a liquid fuel burning system of the type which includes a return fuel flow burner, an automatic air fuel feed control apparatus comprising in combination:

a source of liquid fuel under pressure and a main line connecting said source to the burner;

a source of primary combustion air under pressure also connected to the burner;

means for controlling the amount of air fed to said burner in accordance with the temperature of a substance to be heated thereby;

a diaphragm controlled fuel valve mechanically biased toward closed position;

means connecting said source of air to one side of the diaphragm of said valve to urge said valve toward closed position;

means venting the opposite side of the diaphragm of said valve;

means connecting the return liquid fuel line from said burner to said diaphragm valve in a direction to urge said valve to open position;

means connected to the opposite side of said valve for returning liquid fuel passing therethrough to said source of liquid fuel under pressure;

and means defining an orifice sized to create a predetermined pressure drop connected between said main liquid fuel line and said return line on the burner side of said diaphragm valve; whereby the back pressure in the fuel return line is controlled inversely as the combustion air pressure and a positive fuel flow is maintained for all rates of combustion of the burner.

References Cited by the Examiner UNITED STATES PATENTS 2,397,987 4/1946 Senninger 158-28 2,502,345 3/1950 Ryder 23610 3,076,604 2/1963 Robson 236-10 JAMES W. WESTHAVER, Primary Examiner. 

1. IN A LIQUID FUEL BURNING SYSTEM OF THE TYPE WHICH INCLUES A RETURN FUEL FLOW BURNER, AN AUTOMATIC AIR FUEL FEED CONTROL APPARATUS COMPRISING IN COMBINATION: A SOURCE OF LIQUID FUEL UNDER PRESSURE AND A MAIN LINE CONNECTING SAID SOURCE TO THE BURNER; A SOURCE OF PRIMARY COMBUSTION AIR UNDER PRESSURE ALSO CONNECTED TO THE BURNER; MEANS FOR CONTROLLING THE AMOUNT OF AIR FED TO SAID BURNER IN ACCORDANCE WITH THE TEMPERATURE OF A SUBSTANCE TO BE HEATED THEREBY; MODULATING FUEL VALVE MEANS MECHANICALLY BIASED TOWARD CLOSED POSITION; MEANS CONNECTING SAID SOURCE OF AIR TO URGE SAID VALVE TOWARD CLOSED POSITION; MEANS CONNECTING THE RETURN LIQUID FUEL LINE FROM SAID BURNER TO SAID VALVE IN A DIRECTION TO URGE SAID VALVE TO OPEN POSITION; MEANS CONNECTED TO THE OPPOSITE SIDE OF SAID VALVE FOR RETURNING LIQUID FUEL PASSING THERETHROUGH TO SAID SOURCE OF LIQUID FUEL UNDER PRESSURE; AND MEANS DEFINING AN ORIFICE SIZED TO CREATE A PREDETERMINED PRESSURE DROP CONNECTED BETWEEN SAID MAIN LIQUID FUEL LINE AND SAID RETURN LINE ON THE BURNER SIDE OF SAID VALVE; WHEREBY THE BACK PRESSURE IN THE FUEL RETURN LINE IS CONTROLLED INVERSELY AS THE COMBUSTION AIR PRESSURE AND A POSITIVE FUEL FLOW IS MAINTAINED FOR ALL RATES OF COMBUSTION OF THE BURNER. 